1. Field of the Invention
This invention relates to intimate polymer alloys comprising a major amount of polypyrrolidone and a minor amount of certain linear polyesters and/or polyamides and to processes for preparing such alloys. In a further aspect, this invention relates to processes for preparing such polymer alloys wherein 2-pyrrolidone is polymerized in the presence of the polymer additive. In a still further aspect, this invention relates to processes for preparing alloys of polypyrrolidone and hydrophobic linear polyesters and polyamides via the coprecipitation of polypyrrolidone and the polymer additive from a suitable solvent.
2. The Prior Art
Poly-2-pyrrolidone (also known as nylon-4) is a polymer composed of repeating structure units of the formula: ##STR1##
Polypyrrolidone can be used for making films, sheets, shaped and molded articles, but is primarily of interest for its filament properties. The polymer can be formed into filaments having substantial orientation along the filamentary axis, high tensile strength, and also, because of its hydrophilic properties, closely resembles cotton and silk. In some applications, however, nylon-4 is too hydrophilic, i.e., it is sensitive to a high-humidity environment. Garments may lose their shapes and attain a "clammy" feel. Thus, it would be desirable to produce a polypyrrolidone composition which would obviate or substantially reduce these deficiencies.
U.S. Pat. No. 3,097,181 broadly discloses compositions containing a ratio of polypyrrolidone to non-polypyrrolidone polyamide of from 1:20 to 100:1. This patent is primarily directed to nylon-66 and nylon-6 compositions and describes these nylons as hydrophobic materials. Where the composition is primarily non-polypyrrolidone polyamide, the composition is described as having improved water absorption and dyeing characteristics as compared with the polyamide. Where the composition is primarily polypyrrolidone, the composition is described as having improved fiber forming properties as compared with polypyrrolidone. Although nylon-66 and nylon-6 are described as hydrophobic by this patent, it should be noted that these materials actually have moisture regain values under standard conditions of about 4-4.5 wt% and 4.3 wt% respectively.
U.S. Pat. No. 3,097,181 also broadly teaches that polypyrrolidone may be used in amounts of 1 to 50% with other hydrophobic materials to modify the properties of such materials or such materials may be used in amounts of 1 to 50% with polypyrrolidone. Such materials are described as including the polyesters, e.g. polyethylene terephthalate (Dacron); the acrylics, i.e., polyacrylonitrile-containing materials (e.g., Acrilan, Creslan, Dynel, Orlon, and the like); the polyvinyl resins, e.g., polyvinyl chloride, polyvinylidene chloride, etc.; the polyolefins, e.g., polyethylene and polypropylene; cellulose triacetate; and the like. The only method of preparing the compositions disclosed by this patent is shown in the examples. In the examples, compositions containing polypyrrolidone and either nylon-66 or -6 are prepared by melt-extruding blended powders of these materials. This method is not effective for many of the polymers listed.
Generally, polymer blends are made by hot-melt mixing of particles of each polymer using various mechanical devices such as mills, blenders and extruders to produce the desired degree of mixing. The starting particles are usually of the order of 2 to 6 mm in diameter (weighing 10 to 200 mg). In order to obtain a very well mixed or "intimate" alloy, considerable mixing time, e.g., greater than about 15 minutes, or very high shear rates is required. Such procedures are not satisfactory for poly-2-pyrrolidone because, even though poly-2-pyrrolidone can be melt-spun to high-quality fibers, the residence time must be short, e.g., less than 10 minutes, to avoid excessive thermal decomposition. Similarly, some melt compounding can be done prior to the melt spinning if the residence time is short. If too much decomposition occurs, the molecular weight will be too low, fiber strength will suffer, and filament breaks will occur.
Poly-2-pyrrolidone itself is generally prepared by the alkaline-catalyzed polymerization of 2-pyrrolidone, preferably in the presence of a catalyst comprising the reaction product of a 5-7 membered-ring lactamate and an alkali or alkaline earth metal hydroxide, etc. and a carbon dioxide activator; such as, for example, described in U.S. Pat. No. 3,721,652.
U.S. Pat. No. 3,683,046 discloses what is described as an improvement on the process described in U.S. Pat. No. 3,721,652 and teaches that carrying out the polymerization in the presence of a particulate material tends to increase reproducibility and often produces faster polymerization rates and higher-molecular-weight polymers. Particulate materials suggested by this patent are alkali metal bicarbonates; alkali metal carbonates; particulate charcoal, and particulate material obtained from a partially polymerized reaction mass prepared by polymerizing 2-pyrrolidone in the presence of an alkali polymerization catalyst and carbon dioxide.